In the case of the Danzig parcel cachets, cork (mute) cancels are used to pevent collectors from destroying these cachets, since, as far as I know, at least in my country, the cachets should be saved and stored at the post offices for a certain period of time. That is why these cancels ar named as security cancels as well. I just wonder, what is the situation in the case of the Memel cork (mute) cancels? Are they used for the same reason as on the Danzig cachets?